The acute Whole Effluent Toxicity (WET) test is short term, generally 4 days or less, usually with multiple concentrations. Mortality is the response measured.The chronic WET test runs for a longer period of time, generally 7 days but may be longer, measuring continuous long-term effects such as reproduction for the Ceriodaphnia dubia and growth in the fathead minnow. The chronic test also tests for mortality and may have multiple or single concentrations.

Test conditions and durations of the WET tests vary with the National Pollutant Discharge Elimination System (NPDES) permits. Methods and procedures used to test effluents are strictly defined by the EPA guidelines and Region VIII requirements.

TEST ORGANISMS

Ceriodaphnia dubia
A small invertibrate commonly known as a “water flea” and found throughout most of the aquatic world.

Pimephales promelas
More popularly known as the “fathead minnow” is widely distributed in North America.

Both animals are raised in-house to maintain a readily available source of healthy test organisms. These test organisms are used in Whole Effluent Toxicity (WET) testing for both acute and chronic tests.

List of Acronyms

Acute
A stimulus that lasts a brief time. Acute aquatic toxicity tests last 48 hours for Ceriodaphnia dubia and 96 hours for fathead minnows. Mortality is the response measured.

Bioassay
A test used to evaluate the relative potency of a chemical by comparing its affect on a living organism with respect to a “standard” control.

CO2
Carbon Dioxide

Chronic
A stimulus that lingers. In the case of the ceriodaphnia, the toxicity test continues until 3 broods are born in 60% of the control population. Average number of young is the response measured. Fathead minnow chronic tests last seven days. Growth weight is the response measured.

Composite Sample
Effluent water that is caught over a continuous period of recorded time by a trickle, or by use of an auto sampling device. It may also be a series of grab samples taken at recorded time internals and blended into a single sample.

Control
A treatment in a toxicity test that duplicates all the conditions of the exposure treatments but contains no test material.

Dilution Water
(diluent) Water used to dilute the test water in an aquatic toxicity test in order to prepare different percentages of an effluent. Can be reconstituted or receiving water.

Effluent
A liquid industrial discharge or sewage, which my be released to the environment.

Flow-Thru (system)
An exposure system for aquatic toxicity tests in which the test solutions and control water flow into and out of test chambers or flumes on a once-through basis either intermittently or continuously.

Grab Sample
Effluent or dilution water that is caught in the briefest possible time it takes to fill the rinsed container.

IC
Inhibition Concentration – A point estimation of the chemical concentration that would cause a given percent reduction (e.g. IC25) in a non-lethal biological measurement of the test organisms, such as reproduction or growth.

LC50
Lethal Concentration: 50% – The concentration of pollutant in water to which test organisms are exposed that is statistically or observably estimated to be lethal to 50% of the test organisms.

LOEC
Least Observable Effect Concentration – The lowest concentration in a dilution series having a statistically significant toxic effect (death, reduced fecundity, or curtailed growth) on an exposed population of test organisms when compared to the controls.

NOEC
No Observable Effect Concentration – The highest concentration of a pollutant in a toxicity test that has no statistically significant adverse effect (death, reduced fecundity, or curtailed growth) on the exposed population of test organisms when compared to the controls.

NPDES
National Pollutant Discharge Elimination System

Non-Renewal
Implies that once a toxicity test is set up, it remains undisturbed and unreplaced throughout its total time interval.

Receiving Water
(influent) This is the water that the industry/city obtains for its use before it is processed and becomes effluent.

Reconstituted Water
A water used in culturing and testing animals prepared with de-ionized water and reagent grade chemicals.

Renewal
Implies that the controls and dilution waters are replaced each 24 hours or a static toxicity test.

Screen Test
A preliminary test used to estimate the concentrations to be used in a real test or to observe consistency of an effluent on a routine basis. This test is available and priced according to requirements of the client.

Static (system)
An exposure system for aquatic toxicity tests in which the test chambers contain still solutions of test materials and controls. Tests are static renewal or static non-renewal.